On 02/26/2013 11:11 AM, Russell King - ARM Linux wrote: > On Tue, Feb 26, 2013 at 11:01:30AM -0700, Stephen Warren wrote: >> The conditional in that statement makes me wonder which of the following >> operations will fault in non-secure mode: >> >> 1) Reading from the diagnostic register. > > Won't fault. > >> 2) Writing to the diagnostic register, of a value the same as what's >> already there. > > Will fault. > >> 3) Writing to the diagnostic register, of a value different than what's >> already there. > > Will fault. > >> Would the following not fault in both secure and non-secure mode: >> >> read diagnostic register >> if desired bit already set: >> b 1f >> set desired bit >> write value back to diagnostic register >> 1: > > That is exactly what we do Well, I asked because for the 3 WARs in question at least, that isn't what the code does. For example, from proc-v7.s: #ifdef CONFIG_ARM_ERRATA_742230 cmp r6, #0x22 @ only present up to r2p2 mrcle p15, 0, r10, c15, c0, 1 @ read diagnostic register orrle r10, r10, #1 << 4 @ set bit #4 mcrle p15, 0, r10, c15, c0, 1 @ write diagnostic register #endif (unless that orrle affects the flags and hence skips the mcrle, but I don't think so.) > - the problem is, that if you require > workaround X to be enabled, and a different platform has that errata > fixed, then the other platform will not enable the work-around, and > the bit will be clear. The 3 WARs in question are conditional upon the CPU's revision and patch number (which I'll call rNpN). I assume that any Cortex-A9 with the affected rNpN would require the WAR enabled; is it possible that someone could have fixed a particular core bug directly (and hence not changed rNpN), rather than just updated to a new core revision? If not, the sequence above should be safe, and avoid all the issues you pointed out. I guess anything is possible though. Perhaps this depends a lot on how ARM licenses their cores and fixes and/or if anyone with an architectural license would have applied that to fix a regular A9 core... -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
